1. Technical Field
The present invention relates in general to an improved air bearing design for disk drive sliders and, in particular, to a system, method, and apparatus for a slider air bearing design for improved multiple velocity fly height performance and write element protrusion compensation.
2. Description of the Related Art
Data access and storage systems typically comprise one or more storage devices that store data on magnetic or optical storage media. For example, a magnetic storage device is known as a direct access storage device (DASD) or a hard disk drive (HDD) and includes one or more disks and a disk controller to manage local operations concerning the disks. The hard disks themselves are usually made of aluminum alloy or a mixture of glass and ceramic, and are covered with a magnetic coating. Typically, one to six disks are stacked vertically on a common spindle that is turned by a disk drive motor at several thousand revolutions per minute (rpm).
An HDD also utilizes an actuator assembly. The actuator moves magnetic read/write heads to the desired location on the rotating disk so as to write information to or read data from that location. Within most HDDs, the magnetic read/write head is mounted on a slider. A slider generally serves to mechanically support the head and any electrical connections between the head and the rest of the disk drive system. The slider is typically composed of various shaped pads to glide over moving air in order to maintain a uniform distance from the surface of the rotating disk, thereby preventing the head from undesirably contacting the disk.
Typically, a slider is formed with a set of shaped pads lying over its surface closest to the disk and called the air bearing surface (ABS) along with cavities of various depths surrounding the aforementioned pads and called etched cavities that enable the slider to fly at a constant height close to the disk during operation of the disk drive. A slider is associated with each side of each platter and flies just over the platter's surface. Each slider is mounted on a suspension to form a head gimbal assembly (HGA). The HGA is then attached to a semi-rigid actuator arm that supports the entire head flying unit. Several semi-rigid arms may be combined to form a single movable unit having either a linear bearing or a rotary pivotal bearing system.
The head and arm assembly is linearly or pivotally moved utilizing a magnet/coil structure that is often called a voice coil motor (VCM). The stator of a VCM is mounted to a base plate or casting on which the spindle is also mounted. The base casting with its spindle, actuator VCM, and internal filtration system is then enclosed with a cover and seal assembly to ensure that no contaminants can enter and adversely affect the reliability of the slider flying over the disk.
In some disk drive systems, the slider performance must satisfy seemingly contradictory requirements. One requirement is that the slider must actually fly at a higher fly height when the rotational speed of the disk is reduced to about one-third of the disk drive operating velocity. In one application, the need for this lower velocity arises during the writing of a servo pattern. For example, if the product velocity is about 10,000 rpm and the product fly height is about 10 nm, the servo writing velocity is about 3,780 rpm and the minimum fly height at the outer diameter of the slider is about 11 nm.
In addition to the dual velocity requirement, the slider must provide a flat profile as it scans the disk surface from the inner diameter (ID) to the outer diameter (OD). This flat profile requirement includes a minimum variation in the fly height from part-to-part due to manufacturing tolerances (low fly height sigma), low fly height loss during track seek, and low fly height loss during operation of the disk drive at high altitudes above sea level geographical regions.
A third requirement for these types of sliders is to be able to compensate for write protrusion. At high data writing rates, significant heat is created within the magnetic head. The heat causes material expansion within the magnetic head and slider, which in turn makes regions of the air bearing surface to protrude away from their nominal surface toward the magnetic disk. This protrusion substantially reduces the clearance at the protrusion location, and increases the likelihood of solid contact between the slider air bearing surface and the disk surface. The swelling of the write element reduces the fly height by a significant fraction of the original spacing and therefore creates spacing losses between the slider and the disk.
There have been many attempts to address these requirements in the prior art. Conventional methods vary the air bearing surface structure and include the use of multiple etch depths, shaping of the pads, and shifting the suspension pivot location. Typically, the front end of the rear air bearing pad is made convex or bullet-shaped so as to avoid trapping particles during operation. Alternatively, very deep pockets such as U-shaped designs having an aspect ratio (i.e., depth to width ratio) of 2.0 or greater. Although each of these prior art solutions are workable to some degree, an improved slider air bearing design that more thoroughly satisfies all of the previously described requirements would be desirable.